In a wheel loader or other work vehicle, there is a conventionally known technique for switching a control mode for controlling engine output to a low-output mode and a high-output mode in accordance with the work load (see International Patent Publication No. WO2005-024208). In each control mode, the output of the engine is controlled in accordance with an engine torque curve set in advance. The engine torque curve shows the relationship between the engine rotation speed and the upper limit value of the engine output torque. In relation to the upper limit value of the output torque of the engine, the engine torque curve in the low-output mode is set to be a magnitude of α (α<1) of the engine torque curve of the high-output mode.